wingrass installer: install_msruntime dir not deleted despite rule for it

[hamish]

Hi,

the wingrass installers (all versions) now install the MS runtime dlls if you ask it to. after install it leaves the "install_msruntime" unpack dir behind in \Temp. (also some ms vc++r install files, but MS can fix their own bugs).

I tried different variations of "RMDir" and "Delete", but it doesn't want to go. It's empty, and I don't know if something is cd'd into it or is holding it open.